The present invention relates to above ground fuel storage tanks, and in particular to an above ground storage tank having a removable concrete lid with fireproof seals at joints and openings.
Underground tanks have long been used for the storage and safekeeping of fuels and other hazardous materials. However, due to the long-term effects of groundwater and soil contamination from undetected leakage, the costs of remedial measures, and the related costs of removing underground tanks, underground storage is being avoided in favor of above ground storage of fuels and chemicals.
To provide safe storage of such hazardous materials above ground, storage tanks have been developed for fuels and chemicals where an inner tank is completely encased in an outer concrete jacket. For example, Lindquist et al, U.S. Pat. No. 4,826,644, issued May 2, 1989 shows a steel inner tank for fuels surrounded by both a polyeurethane spacer layer and a polyeurethane liner for secondary containment and, finally, completely entombed in concrete for protection from external hazards.
Cruver et al, U.S. Pat. No. 5,033,638, issued Jul. 23, 1991, discloses an inner steel tank supported by ribs and separated by an air space from an outer concrete casing. The air space is sized at 110% of the inner tank volume, and a sealant may be used on the inner surface of the concrete casing of Cruver et al to provide secondary containment for spills. Again, while the outer concrete casing of Cruver et al is formed from two identical halves, the casing completely entombs the inner tank in the concrete casing. In the event of a spill, loss of secondary containment at the seam between halves is possible.
Above ground storage tanks developed by others for chemical storage use polyethylene inner tanks for primary containment, and polyethylene liners for secondary containment. While effective in resisting chemical substances, polyethylene is expensive, and high mold costs are associated with providing tanks and/or liners for different sizes. Epoxy coatings for outer surfaces of concrete casings are also taught by others for above ground chemical storage tanks.
While generally effective in providing containment, these various above ground storage tanks suffer from a lack of access for inspection, repair and maintenance. Completely encased, the inner tanks may not be repaired or replaced except by destroying the outer casing. While the outer casing of Cruver et al has a horizontal seam between identical halves, access therethrough is problematic. Moreover, disassembly in the event of a spill comprises secondary containment, and may cause high levels of contained -materials to be released. Ready access, while desirable for inspection, repair and maintenance, has not been available due to the hazardous nature of intended uses. Where flammable materials are stored above ground, air gaps in the outer casing are undesirable sources of oxygen which present the possibility that a fire in a nearby structure could involve the stored materials, enhancing the risk of fire and explosion. Gaps or openings through which vapor or spills may leak are also undesirable. Thus, where spills occur in known storage apparatuses, access to clean up spilled material is problematic. As well, repair of damage or decay in the inner tank, or complete replacement thereof, is virtually impossible. Instead, it is necessary to completely dispose of the tank and casing, thus presenting a solid waste disposal problem.
Accordingly, improvements in the design of above ground storage tanks are desired to provide both environmentally sound storage as well as safe access for inspection and economical repair and maintenance.